The present invention relates to shield tunneling machines for continuously excavating tunnels which are not limited to a circular shape in cross section but can be of an optional cross section
Various shield tunneling machines have been proposed and placed into use for excavating tunnels. Generally, such tunneling machines have a cutter disposed on the front side of the machine body. The cutter is rotated about the central axis of the machine to excavate the ground in front of the machine toward which the machine is propelled, and the machine is advanced by an amount corresponding to the amount of excavation. Segment rings are then additionally provided for a further tunneling operation.
Unexamined Japanese Patent Publication SHO 59-102090 discloses a method of shield tunneling with an enlarged cross section so as to form a diametrically enlarged portion locally inside the excavated tunnel to provide a shelter or station.
Such conventional shield tunneling methods and machines are adapted to excavate tunnels by the rotation of the front cutter, so that the profile of excavation is limited to a circular shape only, and difficulties are encountered in excavating tunnels which are shaped otherwise in cross section. On the other hand, the tunnels for sewers, power lines and subways are generally required to have a cross sectional form other than circular in actuality. It has therefore been necessary to excavate the ground with a large circular cross section which includes such a differently shaped cross section. This necessitates an excessive excavating operation and attendant treatment for the resulting muck. The excessive work exerts a greater influence on the tunnel construction cost as the diameter of the tunnel increases as is the case with subways, consequently imposing a limitation on the application of the shield tunneling method.
According to the invention disclosed in the above-mentioned publication, a tunnel of usual diameter is first excavated, and segment rings are assembled. At the location where an enlarged portion is to be provided, the ground is thereafter excavated radially of the tunnel by a special operation, with the segment rings concerned removed. Thus, the disclosed method is not adapted to continuously excavate a tunnel having an optional cross sectional form other than the circular form.